1. Field of the Invention
This invention relates to hybrid electric vehicles and more particularly to drive systems and fuel controllers for such systems.
2. Description of the Prior Art
U.S. Pat. No. 5,789,823 has an engine and/or the electric motor operated to power the vehicle. In order to provide for a desired control of power, a one-way clutch is connected between a lock-up clutch and a start clutch. The arrangement is operative to provide a high torque input from the electric motor through the torque converter turbine to the engine. Once the engine starts, the start clutch is disengaged and the engine drive is directly connected through the one-way clutch that is operative to lock in the direct drive direction so as to power the torque converter impeller or pump. Once full power is transmitted through the torque converter to the transmission, the lock-up clutch is operated to produce a 1:1 drive to the transmission in bypassing relation with the torque converter. In this configuration the one-way clutch is locked up in the drive direction during initial torque converter operation and is operative to free wheel in the drive direction when the electric drive rotor is rotating faster than the engine speed so as to permit overrunning or free-wheeling between the engine and the rotor of an electric motor. Hence, the location of the one-way clutch and its operation is predicated upon an arrangement in which the stator of the electric motor is directly connected to the input housing of the torque converter for propelling the vehicle during various modes of highway operation. There is no provision for lock-up by the one-way clutch during vehicle coasting or during regenerative braking.
While suitable for its intended purpose the arrangement of the one-way clutch in the torque converter of the ""823 patent does not provide for a continuous free-wheel connection between the engine and the impeller or pump of a torque converter in the drive direction and it is not operative to lock upon overdrive from the transmission to the engine during vehicle coasting.
One example operating characteristic of certain prior art torque converters including the combination shown in the ""823 patent is that in operating modes in which the transmission selector is in a forward drive and the accelerator and brake are operated such that the vehicle is coasting down in speed and fuel flow to the engine is reduced to idle speed requirements, the engine can stall or its speed can fall off or droop. In such cases the vehicle driver may feel the pull of the engine when it is restarted in the case of stall or when it is operated to pull back from the drooped speed to the coasting speed of the vehicle as manifested by the vehicle wheels back driving the transmission through the output shaft of the vehicle drive system. Furthermore, advantages of regenerative braking and charging of a battery pack are lost if the engine must be restarted.
Other hybrid electric motor and internal combustion engine drive systems in a hybrid electric vehicle (HEV)are shown in U.S. Pat. Nos. 5,637,987 and 5,698,905. The ""987 system includes an energy management control that selects either gas engine or electric motor drive depending upon the vehicle drive mode. The control for the ""987 patent does not control the HEV by sensing vehicle speed in a brake start speed range; a hysteresis speed range and a xe2x80x9cregen-ablexe2x80x9d speed range by use of a brake pedal position and pressure sensing sequence. The term xe2x80x9cregen-ablexe2x80x9d is coined to indicate that regenerative braking is possible. Additionally the ""987 patent requires a gear set interposed between an engine and a transmission to manage the energy provided to drive the vehicle. The ""905 system includes a gas engine but it is used to power a generator for producing a source of electric current for driving an electric motor that constitutes the drive for the vehicle. Neither system provides for an aggressive management of fuel flow to a gas engine during vehicle coasting operations in order to improve total fuel consumption. Furthermore, neither system discloses or suggests that the internal combustion engine be directly coupled to a transmission drive that is operative to supply primary power to a wheeled vehicle above a predetermined vehicle speed.
Additionally, the prior art systems do not provide a method for controlling fuel flow in a system that is configured to prevent engine stall so as to avoid the need for electric motor restart of an engine following a coasting mode of forward speed operation when the engine speed falls below a selected drop-to-neutral speed.
Furthermore, the prior art systems do not provide an internal combustion engine and electric motor combination that is normally coupled in parallel driving relationship to a drive transmission of a wheeled vehicle and wherein the electric motor can be used to start the engine and can be conditioned in response to brake pedal pressure to cause a proportional regenerative braking for charging a battery pack that can be used when the vehicle is stopped to operate the electric motor for starting the internal combustion engine.
The present invention includes a hybrid-electric vehicle (HEV) that has an internal combustion engine connected to drive a multi-speed automatic transmission that can if desired include a torque converter.
Additionally the HEV includes an electric machine having a rotor connected to the crankshaft of the engine and a stator and a controller for selectively controlling the electric machine to serve as an electric starter or as a generator for regenerative braking during vehicle drive so as to charge an associated battery pack. A fuel controller is provided that is operative in response to vehicle braking and further is operative to respond to vehicle speeds in different ranges to improve fuel consumption characteristics of the vehicle.
The advantage of such a drive arrangement is that a fuel control can be provided that will entirely cut off fuel flow during vehicle decelerations and stops. The integration of an electric motor directly connected to the crankshaft of the internal combustion engine allow the shut off of fuel and restart of the gas engine to be conducted virtually transparent to the driver.
The control of the gas engine and the electric motor is according to routines that operated in conjunction with the usual operation of an engine driven automatic transmission system for driving the wheels of a vehicle. In such systems the engine is driven by an electric motor starter and fuel is supplied during an engine startup mode. The transmission is placed in a drive mode and the vehicle is accelerated by depressing an accelerator pedal for supplying more fuel and air to the engine. When the vehicle is up to speed the torque converter lock-up clutch is applied and the transmission is, for example, in a forward speed selection position such that the vehicle cruises under the power of the gasoline engine and if desired, a portion of the cruise power can be supplied by the electric motor (especially at lower startup speeds).
In such systems, when the accelerator pedal is released, the fuel can be cut depending on vehicle speed and gear setting. Above a prescribed vehicle speed, if the torque converter clutch is locked or if a reverse locking one-way clutch is operable to lock the turbine and impeller of a torque converter as set-forth in copending U.S. Ser. No. 09/483,987, office file H-204481, the electric motor can be controlled to deliver regenerative braking during decelerations to recharge a battery pack.
Under one control routine, when the brake pedal is depressed a brake sensor is operative to produce a signal that is processed by a microprocessor to maintain the fuel fully cut-off for the entire deceleration of the vehicle while in the regen-able speed range of operation.
In a lower speed range of vehicle speeds in the brake-start range of operation, if the brake pedal is released during deceleration, the engine can be restarted with the release of the brake pedal and a re- supply of fuel.
In accordance with another aspect of the invention when the vehicle speed is in a creep speed range as in the case of a usual vehicle launch, the fuel is not cut off on either braking or accelerator pedal release until the road speed of the vehicle exceeds a prescribed threshold, e.g., exceeding a maximum hysteresis speed.
Thus an object of the present invention is to provide a fuel management control method for a hybrid electric vehicle drive having a transmission with gear settings, an internal combustion engine and an electric motor arranged in parallel such that both can propel the vehicle; the system including an electric motor driven fuel pump and a programmable microprocessor the method comprising the steps of monitoring vehicle speed; sensing braking pressure; shutting-off fuel flow to the gas engine in response to vehicle braking at predetermined vehicle speeds and gear settings and maintaining the fuel shut off during vehicle coasting while controlling the electric motor to provide either engine starting or regenerative braking depending upon the vehicle speed.
Another object of the invention is to provide an improved method of fuel control for a hybrid electric vehicle including a drive system with an internal combustion engine and an electric machine operated as an electric motor to electrically turn the engine so as to electrically creep start the vehicle without supply of fuel or spark to the internal combustion engine and as a generator to produce regenerative braking and wherein the electric motor is connected via a drive belt to the crankshaft of the engine and wherein fuel is cut-off in accordance with an aggressive fuel control algorithm responsive to brake pedal operation in a brake start speed range and in a hysteresis speed range and to a combination of gas pedal position and brake pedal position in speed ranges above the hysteresis speed range.
A feature of the present invention is to, if desired, provide a torque converter having a mechanical one-way clutch connected between the pump and turbine of the torque converter that free wheels in the input drive direction so that the engine can be started by the electric motor and wherein the one-way clutch locks to directly connect the torque converter turbine and impeller during any back drive produced during vehicle coasting to prevent engine stall.
A further feature of the present invention is to initiate such fuel control when the vehicle transmission is in a forward drive mode and decelerating.
A feature of the present invention is to initiate such fuel control when the vehicle transmission is in a forward drive mode and decelerating upon application of a brake pedal.
A feature of the present invention is to initiate such fuel control when the vehicle transmission is in a forward drive mode and decelerating upon release of an accelerator pedal.
Still another object of the present invention is to provide an improved method for operating a hybrid vehicle having an internal combustion engine; a torque converter with an impeller turbine connection through a forward drive free wheeling and reverse drive locking one-way clutch connection and an electric motor generator connected to the crankshaft of the internal combustion engine by a direct drive belt and controlling the electric motor to charge batteries during vehicle deceleration/coasting operation and providing an engine fuel controller and operating the controller to be responsive to vehicle operations causing coasting to provide an aggressive fuel flow cut-off while the torque converter is operative to synchronize overdrive of the vehicle during coasting with the engine speed to prevent the internal combustion engine from stalling upon fuel flow cut-off during such coasting operation.
Yet another feature of the invention is to provide a fuel management control method for a hybrid electric vehicle drive having an internal combustion engine and an electric motor arranged in parallel such that both can propel the vehicle; the system including an electric motor driven fuel pump and a programmable microprocessor the method comprising: providing a belt drive connection between the electric motor and the engine; providing a torque converter with an impeller turbine connection through a forward drive free wheeling and reverse drive locking one-way clutch connection in the vehicle drive and controlling the electric motor to charge batteries during vehicle deceleration/coasting operation and during regular cruising if the battery state of charge is low and cutting off fuel flow to the engine in response to either gas pedal or brake operation while the torque converter is operative thereby to synchronize overdrive of the vehicle during coasting with the engine speed to prevent the internal combustion engine from stalling upon fuel flow cut-off during such coasting operation.
A further advantage is that during decelerations from a regenerative braking speed range referred to as a Regen-Able speed range, the fuel flow can be cut off when the accelerator pedal is released, or when the brake pedal is depressed depending on the vehicle speed and gear setting. In this routine, as the vehicle continues to roll forward, the electric motor""s polarity can be reversed to activate regenerative braking which helps decelerate the vehicle and recharge an associated battery pack. The torque converter clutch 105 or the locking clutch 34 is kept active in the Regen-Able speed range so as to keep the gas engine spinning so that the engine firing can be easily restored if the accelerator is depressed.
A still further advantage is provided by the fuel control and hybrid system of the present invention as the vehicle decelerates down to a low speed range (e.g., xe2x89xa610 mph), hereinafter referred to as the xe2x80x9cHysteresis Modexe2x80x9d. In this mode when the brake pedal is depressed when decelerating from a speed greater than the minimum Hysteresis speed, the fuel is cut off. However, in this mode, once driving in or below the Hysteresis speed range, the fuel is not cut off until the vehicle speed exceeds the maximum Hysteresis-range speed. This fuel control operation provides enhanced low-speed driveability.
A further feature is to provide such method of control in a hybrid vehicle gear having a multi-transmission and wherein in higher gear (e.g. 3rd and 4th) and above a critical speed Vtps release of the gas pedal initiates an engine fuel-off sequence.
Another feature is to provide the preceding fuel control sequence including the step of providing a timer that delays the beginning of the fuel cutoff sequence.
Still another feature is to provide such timed control of fuel shutoff including shutting off fuel, one cylinder at a time to provide a smooth deceleration feel. For lower gears (e.g. 1st and 2nd) and under a critical speed, fuel cutoff is initiated by the application of the brake pedal.
A still further feature is to provide such method of control where, at some high speed, if the fuel is shut off (by either release of gas pedal or application of brake), and the driver coasts with no pedal application, a reverse freewheel will back-drive the engine until some low engine RPM at which the compression pulses of the engine become objectionable; the transmission operative to drop to first gear (effectively neutral since the first gear has a freewheel). And wherein fuel and spark is delivered to the engine just before this drop-to-neutral point so as to not stall the engine; the drop-to-neutral point being calibrated as a function of deceleration rate.
A further feature is to provide the preceding method including the step of restarting a stalled engine from a no-pedal condition by applying the gas pedal.
A further method includes providing a micro processing program including a xe2x80x9chybrid-active speedxe2x80x9d as the speed that the car needs to exceed for the hybrid system to become active (i.e. fuel cutoff enabled); and wherein a speed hysteresis is included in the hybrid-active speed having a hybrid-active speed for acceleration Va, and having another for deceleration Vd and wherein the quantification of acceleration/deceleration determined by whether the driver has applied the gas pedal just before the fuel-off command.
A further feature is a method in fuel control in an HEV by providing a brake start routine at gas engine start-up can be activated from vehicle stop by the release of the brake pedal without requiring depression of the accelerator pedal; providing a brake pressure sensor and on a powertrain computer for tracking the pedal force, as well as the rate of pedal application and the rate of pedal release. Wherein from a full vehicle stop (or low-speed vehicle roll operation, with the engine stalled) upon release of the brake pedal, the engine and transmission is turned by the electric motor. A further feature is to provide such a method wherein a powertrain computer controls the engine acceleration and speed, and delivers fuel and spark based on engine speed, vehicle speed, throttle position, and intake manifold air pressure (MAP).
A further feature is to provide a method including determining if the engine temperature is above a prescribed threshold and controlling the starter such that the engine does not have to be re-cranked. When the ignition key is turned to run (but not all the way to crank) and PRNDL lever is shifted into drive (D) and the brake pedal is released, the electric motor operating creep the vehicle forward and start the engine as fuel flow commences.
Yet another feature is to provide such a method including monitoring engine temperature, road grade, and vehicle turning to adjust the calibration of the hybridization or the level of drive required from the electric motor and from the gasoline engine during such creep forward operation; wherein when the vehicle is cold, the fuel is not turned off and on to optimize fuel consumption since electric motor start only would constitute an unnecessary drain on the battery pack and wherein when the road grade is too great the fuel is not cut off, additionally, the fuel cutoff algorithm is readjusted when making hard turns (at speed) or tight turns (at low speeds) to enhance driveability.